1. Field of the Invention
This invention relates to an absorbent article for absorbing body fluids such as menstrual fluid, vaginal discharge and/or urine. More particularly, this invention relates to an absorbent article that is particularly well suited for absorbing menstrual fluid that is discharged in gushes. The remainder of this specification will discuss application of this invention to absorb menses and other vaginal discharges. However, the teachings are equally applicable to incontinence products as well.
2. Prior Art
Conventional full-size sanitary protection products, and other feminine hygiene products such as adult incontinence devices, typically contain an absorbent element, a fluid-pervious body-contacting element and a fluid-impervious undergarment-facing element. The principle function of such articles is to absorb body fluid, such as menstrual fluid, from the wearer and retain the fluid in order to prevent the fluid from soiling the wearer's garments. Such products are designed primarily around the premise that, for example, menstrual discharges are constant and even with a relatively low average flow rate. Such products are also designed around the premise that menstrual fluid, specifically, is a low viscosity liquid that behaves much as water behaves when exposed to an absorbent fibrous material. Thus, the materials of sanitary protection products typically used in products today, although capable of absorbing relatively large quantities of low viscosity fluid, tend to absorb such fluid at relatively slow rates. More viscous fluid are absorbed even more slowly or sometimes not at all. Thus, theoretically, sanitary napkins have the capability of absorbing between 50 and 100 grams of fluid. However, soiling may occur after only 5 to 10 grams of fluid are deposited on the absorbent article. Two of the primary reasons why soiling occurs is that conventional napkins do not have the ability to absorb fluid that is discharged at a high flow rate, and they are designed to absorb fluid that behaves like water rather than a fluid containing 85% solids.
It is commonly known that menstrual fluid is composed of blood that comes from the blood vessels of a woman's endometrium. It is also known that menstrual further contains fragments of endometrial tissue, mucus from the vagina and cervix, minerals, and protein. It is thicker and darker red-brown than blood from a vein and is about 85% solids and 15% water. Solids include endometrial tissue and red and white blood cells which together form aggregates that are commonly referred to as "clots." Menstrual fluid is highly viscoelastic with viscosity decreasing only upon the application of shear, such as that applied between a woman and a sanitary napkin.
It is also commonly known that about 76% of the menstrual flow occurs during the first three days of menses, with the most profuse bleeding occurring on the second day. During this time, menstrual fluid is often discharged in gushes that can total approximately 4 cc of fluid in a matter of seconds. This often occurs in the morning, just after awakening. During the night, and depending on the position one assumes during sleep, menstrual fluid can collect in the vagina. Upon standing, this fluid will then exit the vagina at a relatively fast flow rate. This phenomenon can also occur after sitting for long periods of time.
The main absorbent portion of conventional sanitary napkins comprise some material that has an ability to absorb a large quantity of a low viscosity fluid. The most prevalent material in use are wood pulp fluff and wood pulp fluff used in conjunction with sphagnum and superabsorbent polymers, where the latter is based primarily on acrylic acid. In the case of sphagnum, fluid is absorbed by a high capillary pressure which draws fluid into the capillary structure. In the case of a superabsorbent polymer, a concentration of fluid in the polymer is created. The fluid causes the polymer to swell, and as it swells it allows more fluid to be absorbed until its capacity is reached when it is fully swollen.
One problem exhibited by products using either sphagnum or superabsorbent polymer is that the time necessary for either sphagnum or superabsorbent polymers to absorb the fluid is many times longer than the short time during which a relatively large quantity of fluid is deposited on the napkin in a gush. As a consequence, the fluid will pool on the top of the napkin before it can be completely taken up by the absorbent material. If the fluid pools, there is very little that can contain it until it is absorbed. Therefore, the chances that the fluid will run off the napkin is very great.
Conventional products on the market, and the prior art upon which these products are based, try to overcome this inability to absorb gushes by interposing a transfer layer material between the cover and the absorbent core. The purpose of this transfer layer is to act as a fluid transfer buffer layer by quickly drawing fluid from the cover, to hold it until the absorbent core can take absorb it, and then to transfer it to the absorbent core. However, these products still depend on wicking into the cover, between the cover and transfer layer, and between the transfer layer and the core. The time needed for the fluid to rapidly and fully pass through the cover, to fully wick into the transfer layer, and then to wick into the core is still sorely insufficient to absorb a large gush. Therefore, the chances for failure remain. All of the components in this fluid transfer chain, starting with the cover and continuing on to the transfer layer and absorbent core, inhibit the rapid and complete transfer of large quantities of fluid. Further, such products have a close fibrous network, with ever decreasing pore size openings as one proceeds further into the thickness of the product, that increases capillary pressure and ability to wick low viscosity fluids such as water. Thus, what is obtained is a fibrous structure that can draw a fluid into it but restricts the absorption of solids such as those present in menstrual fluid.
The primary object of this invention is to overcome these deficiencies in the prior art.